In exploration and extraction of hydrocarbons, such as fossil fuels (e.g. oil) and natural gas, from underground wellbores extending deeply below the surface, various downhole tools are inserted below the ground surface and include sometimes complex machinery and explosive devices. Examples of the types of equipment useful in exploration and extraction, in particular for oil well drilling applications, include logging tools and perforation gun systems and assemblies. It is often useful to be able to maintain a pressure across one or more components, (that is, to provide a “pressure barrier”), as necessary to ensure that fluid does not leak into the gun assembly, for instance. It is not uncommon that components such as a bulkhead and an initiator are components in such perforating gun assemblies that succumb to pressure leakage.
Upon placement into the perforating gun assembly, one or more initiators, (typically a detonator or an igniter), have traditionally required physical connection of electrical wires. The electrical wires typically travel from the surface down to the perforating gun assembly, and are responsible for passing along the surface signal required to initiate ignition. The surface signal typically travels from the surface along the electrical wires that run from the surface to one or more detonators positioned within the perforating gun assembly. Passage of such wires through the perforating gun assembly, while maintaining a pressure differential across individual components, has proved challenging.
Assembly of a perforating gun requires assembly of multiple parts, which typically include at least the following components: a housing or outer gun barrel within which is positioned a wired electrical connection for communicating from the surface to initiate ignition, an initiator or detonator, a detonating cord, one or more charges which are held in an inner tube, strip or carrying device and, where necessary, one or more boosters. Assembly typically includes threaded insertion of one component into another by screwing or twisting the components into place, optionally by use of a tandem-sub adapter. Since the wired electrical connection often must extend through all of the perforating gun assembly, it is easily twisted and crimped during assembly. Further, the wired electrical connections, to a detonator or initiator, usually require use of an electrical ground wire connectable to the electrical wire and extending through the housing in order to achieve a ground contact. When a ground contact is desired, the electrical ground wire must also be connected to an often non-defined part of the perforating gun assembly. Thus, the ground wire is sometimes wedged on or in between threads of hardware components and/or twisted around a metal edge of the housing of the perforating gun assembly. One issue with this arrangement is that it can be a source of intermittent and/or failed electrical contact. In addition, when a wired detonator is used it must be manually connected to the electrical wire, which has lead to multiple problems. Due to the rotating assembly of parts, the electrical ground wires can become compromised, that is to say the electrical ground wires can become torn, twisted and/or crimped/nicked, or the wires may be inadvertently disconnected, or even mis-connected in error during assembly, not to mention the safety issues associated with physically and manually wiring live explosives.
According to the prior art and as shown in FIG. 1, a wired bulkhead 10′ of the prior art is depicted. In a perforating gun assembly, the bulkhead 10′ may be utilized to accommodate electrical and ballistic transfer (via wired electric connection 170′, shown with an insulator 172′ covering one end of the electrical contact component 20′, which extends through the body of the bulkhead 10′) to the electric connection of a next gun assembly in a string of gun assemblies, for as many gun assembly units as may be required depending on the location of underground oil or gas formation. Such bulkhead assemblies are usually provided with fixed pin contacts extending from either end of the assembly. Typically the bulkhead is employed to provide the electrical contact or feed-through in order to send electrical signals to the initiator or a type of switching system. In such applications, the pressure bulkhead is required to remain pressure sealed even under high temperatures and pressures as may be experienced in such applications, both during operation and also after detonation of the perforating gun, for instance, so that a neighboring perforating gun or downhole tool device does not become flooded with wellbore fluid or exposed to the wellbore pressure. Maintenance of the pressure differential across such devices occurs via usage of rubber components including o-rings 32′, rubber stoppers and the like.
Such bulkhead assemblies are common components, particularly when a string of downhole tools is required, and is a barrier or component through which electronic componentry and/or electrical wiring and electrical ground wiring must pass, (e.g. electric feed-through), and a need exists to provide such componentry with electric feed-through while maintaining a differential pressure across the component, and without compromising the electrical connection.
Improvements to the way electrical connections are accomplished in this industry include connections and arrangements as found in commonly assigned patent applications PCT/EP2012/056609 (in which an initiator head is adapted to easily introduce external wires into the plug without having to strip the wires of insulation beforehand) and PCT/EP2014/065752 (in which a wireless initiator is provided), which are incorporated herein by reference in their entirety.
The assembly described herein further solves the problems associated with prior known assemblies in that it provides, in an embodiment, an assembly that allows improved assembly in the field while maintaining the integrity of the electrical connection, as described in greater detail hereinbelow.